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Elite Veteran
  
Location: Oceanside, CA | I've been playing with my tune to try and zoom in as close as i can to fuel level indication/capacity/range.
While the FMC specs say the tank is 60 gallons, it seems to me that the few times I've ran it really(really, really) low I've struggled to get any more than 50gallons it it.
Anyone else had similar experience?
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Expert
Location: Cottage Grove, OR | I have filled with over 50 gallons a time or two. I know that for some reason coach 617 has s smaller than stock tank. Can you get some good dimensions of the tank? Can then do a calculation and see if you have a non-standard tank. |
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Extreme Veteran
Location: Scottsdale, Aridzona | Hmmmm . . . I measured the stock gasoline tank on my FMC #120. I think it is stock, I have nothing to make me think otherwise.
It measures (outside) 28.5" (fore/aft) X 25" (wide) X 20" (deep) from the bottom of the tank to the bottom curve of the filler neck at the "outside" where the gas tank cap fits on.
Those dimensions multiplied together to give 14,250 cubic inches of liquid volume . . . before it starts spilling out the filler neck.
14,250 divided by 1,728 cu in per cu ft gives 8.24 cubic feet max volume . . . times 7.4805 gallon per cubic foot . . . gives 61.5 gallons.
I ignored the wall thickness of the tank, undercoat, dirt so 61.5 gallons outside probably is 60 gallons "inside", close enough to the FMC Factory Spec of 60 gallon gas tank for me.
There is a 4" wide 45 wedge removed from the top outside edge of my tank, behind the gas door, that the fill neck sticks straight into as it sticks down into the tank.
There is more "tank" above the filler neck that you can see if you peel some small section of the grommet around the fiberglass at the filler neck.
The tank can ONLY be filled to the outside bottom of the filler neck . . . or it starts spilling out !
My filler neck, from the cap flange down at 45º, to the end of the fill pipe, is 6 inches.
Me and Capt. Queeg proved beyond the shadow of a doubt and with... geometric logic... that the vertical height of the bottom of the fill pipe is 4.24 inches (right Isosceles triangle with 6" hypotenuse).
So if 60 gallons of strawberry juices come to the top of the bottom of the filler neck up at the cap . . . then each vertical inch of total volume holds . . . 60 gallons divided by 20" . . . 3 gallons per vertical inch.
So to get 60 gallons in the stock FMC tank, it has to be filled to the bottom of the outside part of the neck, just before it spills out.
Stopping the fill one vertical inch from the top of the pipe/cap flange "lowers" the fill to only 57 gallons . . . 2nd vertical inch "lowers" fill to 54 gallons . . . 3rd vertical inch "lowers" fill to 51 gallons . . . and the 4th vertical inch, which would be essentially at the bottom of the 45º 6 inch fill pipe sticking down in the tank, "lowers" fill to 48 gallons.
Ah Ha ! There is a reason that most FMCers can't get 60 gallons in the stock FMC gas tank.
It would have to be filled till it was just about to spill out ! We all want some expansion, vent space in the top of the tank . . . so we stop the fill down in the neck.
I'm sure the FMC "design engine ears" made the biggest gas tank they could fit in there, with suitable expansion/vent space . . . then the "Sales Dept" printed the 60 gallon Fuel Tank Spec, and said not to say anything that if you did put 60 gallons in it . . . you would probably spill it before you got the pump shut off, and also not tell that the auto shut off fuel nozzles would "click" off some place "down" the pipe.
So how the devil do I tell my fuel consumption ???
I have said many times . . . fill the tank until you can see the gas in the filler neck. Stop filling at some LEVEL/SPOT that you can remember more than an hour. Write down odometer miles. Go drive at least 50 miles . . .100, 200 miles. Fill the tank to the SAME LEVEL/SPOT in the filler neck . . . then write down that GALLON(s) amount. Write down the just filled odometer miles. Subtract the previous from the now mileage . . . and divide those miles by the Gallons that you just refilled the tank to the SAME LEVEL/SPOT. That is the MILES PER GALLON that your FMC got on the trip you just completed sitting there in some gas station. Gallons used to refill to the SAME LEVEL/SPOT. That is real tank fuel consumption for those miles. No computers, no satellites, no special computer devices or "performance" programs. What ever your odometer and the State checked Pump saw for gallons is real. However you drove those miles . . . fast, slow, uphill, downhill, backwards, to Grand Ma's . . . that is the fuel consumption for your FMC for however many miles that "trip" was. You may not like the answer . . . but as long as your odometer is pretty close . . . and the State certifies the Gallons delivered by every pump . . . that is the MPG your FMC gets . . . whether the fuel is gasoline, diesel, kerosene, JP-4, JP-6, JP-8, hydrazene, or NITROMETHANE ! Understand how to really measure Miles per Gallon that YOUR FMC gets ?
Oh, one last thing . . . you do need a pencil and some paper to write the mileage and gallons down . . . and subtract two numbers and divide one number into another. I have used those 3 X 5 spiral bound little blank books. I have all the gallons and miles and date for every car I have ever owned since I bought them, with every oil/filter change, new battery, new tires, new belts, and "other" maintenance, in a book for each vehicle, that STAYS in that vehicle. It is very handy to calculate the Fuel Consumption in Miles per Gallon at EVERY fillup . . . and then you have a ready reference . . . the previous entry ! . . . when you may notice that . . . hey, my mileage went DOWN X Miles per gallon. WHY ?
Fill UP ! Lou #120
Edited by hemi354az 2017-08-02 11:44 PM
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Veteran
Location: Olympia, Washington | One more statistic to add, they can run out of gas for 3 to 5 miles due to the large flat bottom on the tank. Yes that is from personal experience. |
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Expert
Location: Cottage Grove, OR | And if you are very low on fuel trying to make it to the next town in Montana and encounter a steep grade, you can run out of fuel very quickly when it all runs to the back of the tank! Yes, personal experience! |
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Extreme Veteran
Location: Scottsdale, Aridzona | That is why I drive by the TRIP ODOMETER not the gas gauge. Since I know what my miles per gallon is . . . I can figure out how far 45 gallons will take me . . . and act accordingly. It does not cost anymore to fill the top 75% of the tank than the bottom 25% . . . but the consequences of any "variability" of the later can be avoided.
Refill ON! Lou #120 |
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Extreme Veteran
Location: Scottsdale, Aridzona | The next town in Montana ? That could be more than a day away ! |
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Elite Veteran
Location: Oceanside, CA | http://www.fmcowners.com/mbbs22/photos/show-album.asp?albumid=127&p...
Lou,
Thanks, you did the math that I had figured I would have to do, figuring that I typically fill it to a couple inches below the spill out I'm in the 54gallon range which matches what I've seen.
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Realistic Maximum Fuel Fill
